coax length

Okay i think i am more confused than i was when i started reading this thread


Here my deal...

on my 4 wheeler i have a Wilson 2000 trucker antenna with it mounted on the fender with the dodge ram mount roof mount is not an option as the truck wont fit in the garage and a few other places. My CB is mounted under the dash right next to the 4x4 shifted... i figured out that it is about 6ft from my antenna to the CB.

Now i plan to buy my own coax as i had RadioShit (Opps i mean shack) coax in there that was leaving me with a SWR of 2:1. I borrowed a friends coax and got a 1.3:1 but, i forgot to notice the length

So would i have better results with a 9ft or 18ft coax?

 

Nutshell answer? No, no, and NO! this 1.3 is FINE and further illustrates that trimming coax is bunk. Even if you could get the SWR better, the difference in 1.3 and 1.1 is not even measurable; not worth fiddling with.
Forget about all this coax length hooey! The way to tune an antenna is by setting up the ANTENNA ITSELF to the proper frequency, properly grounding the thing to the body, and forget about coax length! That is an old CB myth, and few other operators in any other radio service BUT CB ever even worry about coax length. It is an old wives' tale that was born on CB and lives forever there! If you can "tune" the antenna by trimming coax to a certain length, there is something ELSE wrong that is being masked. You will STILL have a poor-performing antenna system if you can get the SWR down just by trimming coax! SWR is not there is to it. You can "load" up a 10 watt, 50 ohm resistor and get 1.1 ratio! You won't have much of a signal, but you'll have a bang-up SWR'sssssssssssssssss!

You are fine as is; leave it alone!

GF

 

Well the 1.3:1 was gotten with a friends borrowed coax to see if indeed it was my coax so, i can't leave it alone as i have to get my own.. that's why i was wondering if i should get 9ft or 18 ft

 

the way to test coax is to put a known good dummy load on one end and a radio with a SWR meter on the other...

A good run of coax will read under 1.2:1 ..... loss if you want to measure it will be small at CB.

I tested RADOSHACK RG-8 and LMR-400 both 100 foot long on 446.000 MHZ. With 10 watts into the coax and a bird#43 and milspect dummy load at the other end of the coax the LMR-400 got about 6 watts to the bird meter the RADIOSHACK only about 4 watts ....

The same test with 100 foot of RADIOSHACK RG-8X I got about 1 watt a 10 db loss per 100 foot ...

 

sorry to be a noob but what consists of a dummy load?

 

No your question is a good one .......

A dummy load is a 50 ohm load that looks like a very low SWR to a radio ....

In this case you put it on the OTHER end of the coax from the meter and radio and IF the coax is good it will show the dummy load through the coax as a good match ....

IN SHORT .....

a 50 ohm dummy load at the end of 100 foot of 50 OHM coax should be 1.2:1 or less .... NOW if you REPLACE the dummy load with a working 50 ohm antenna it should read the same .....

The SWR of your system should be set by the LOAD at the end of the coax.

 

So in a nutshell its the same as putting a 75 ohm F terminator on the end of a RG6 coax to test if it is good.. just that i need a 50 ohm terminator to test the CB coax... correct? (i install Directv..lol)

 

CORRECT ... 75 ohm is standard for CATV TV and cable work 50 ohm is for CB/HAM

 

Some how I'm totaly lost

I answer a question with a simple answer and how it got to that responce is beyond me ....

IF you run enough coax on 1750 meters you will run out of power at the end .... the total loss will get to 99.99999% at some point ...... and yes you will show a 1:1 swr due to return loss being so high ....

IF your antenna is working right you will have a good match .... just like that dummy load .... this is a fact .....

Cutting coax that is 50 ohms into a 50 ohm antenna is not going to match anything .....

The last time I used a smith chart was in the R&D lab at Sperry microwave
more than 30 years ago ..... and that was on 96 GHZ ......

Now to let my brain cells cool down ....

 

Originally Posted by Channel Jumper
"I got a Question and I would like a honest answer.
Is it that truckers are so G.D dense that you can tell them something and it goes in one ear and out the other?
Or is it just some type of CB radio mentality?

I wrote a whole article on this forum about SWR, but for some reason - people are too stupid to read it, and people are too stupid to understand that there is no difference between my antenna and your antenna.
You people are just spinning your wheels - wasting good money after bad on this junk when the most you can talk is a couple of miles with your CB radio mobile."

An honest answer is in itself a question. With cursing, talking down to, name calling, in general disrespectful and terrible treatment and expressed opinion of CB'ers and truckers, why do you come here to a truck driver CB forum? This is the real question which needs answering CJ. Respect is earned not given and the level of disrespect you dish out makes all of your so called knowledge void. Many people come here and unlike you have a life meaning no time to search for posts you have previously made talking to other people about a subject they had no need to know before they encountered a problem and came here seeking help from hopefully someone who does not have the personality of a rope such as yourself.

The endless expression of your opinions concerning CB in a negative light do not belong on a forum where people come to discuss a hobby they find enjoyable. Joy being the key word here, something I am quite certain you strip from all you encounter. By the way if CB is so bad why do you talk with a positive way about 10 meters which is only 1 to 2 MHZ above CB. After all you keep telling people to throw out their CB's yet you seem intent on keeping your 10 meters which based upon your opinion should therefore be just as useless as CB considering their relative proximity in frequency.